For the lubrication of vehicles and/or machines of different kinds, so called single pipeline systems are often used that work with pressure sequences in an arrangement of conduits that lead from a pressure producer or feeding pump to those separate metering devices or elements, which are included in the system to a number that agrees with the number of lubrication points. The most simple metering element consists of a restriction in the form of a calibrated orifice. At a given pressure difference a metered amount is dispensed by this kind of element, which amount is a function of the area of the orifice, the viscosity of the lubricating medium and the duration of the pressure. This kind of metering element is however generally considered to be too inaccurate.
In order to obtain good accuracy it is required that the metering element meters a given volume of medium independently of variations in the pressure, of the viscosity of the medium and of the tolerances in the metering element.
Metering devices of the above described kind are disclosed in the U.S. Pat. Nos. 1,897,609 and 2,000,925. These designs do however not function satisfactorily. The metering element does not have any stable sealing function of the "sluicing cone" of the metering piston.
In the design according to U.S. Pat. No. 1,897,609, the piston element in question floats freely in its associated chamber without any hydrostatically defined position in relation to the cone in question. This means that the piston will oscillate in every intermediate position in relation to the cone. In the end positions other conditions arise and mechanical stops and hydrodynamic forces influence the function. The essential factor, from the functional point of view, is however that the metering piston is not "tight" in its path between the end positions, which results in that an indefinably larger amount of lubricant than intended being discharged.
In the design according to U.S. Pat. No. 2,000,925 an attempt has been made to remove this drawback by introducing a spring that is intended to forcibly close the cone against the piston. In this case as well, however it is impossible to make this solution stable. In order to meet the two functional conditions at the discharge and at the return, certain conditions have to be met. The requirements thus are that the cone has to be closed at the discharge and open at the return. If the spring force is chosen to correspond to the pressure difference across the piston, between inlet side and outlet side, this cone will also oscillate. In the other cases the cone will have a distinct position, open or closed.